Heat radiator, device for infrared welding and method for heating plastic components

ABSTRACT

The present invention discloses a heat radiator, especially an infrared radiator, having at least one radiation source by means of which supplied electrical energy is convertible into heat radiation, as well as a control. This control comprises at least one frequency converter having a first, a second and a third output so that between the first and the third output a first alternating current is providable and between the second and the third output a second alternating current is providable by means of which the at least one radiation source is operable.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the priority of German patent application DE 102013 216 021.6, filed on Aug. 13, 2013. The entire content of thispriority application is incorporated herein by reference.

TECHNICAL FIELD

The present invention is related to heat radiators, especially aninfrared radiator, a device for infrared welding of at least two plasticcomponents as well as a method for heating or welding at least oneplastic component.

BACKGROUND

In the last years, the welding of plastic by means of infrared radiationhas gained currency. Here, the plastic parts to be welded are heated andjoint thereafter in the area of the weld seam by means of infraredradiation. The advantage of this technology compared to friction weldingmethods, as for example vibration or rotation welding, consists amongothers in the avoidance of the dust and fibre particles coming up in thedry rubbing phase. These particles contaminate and affect the weldedjoint to be produced. Further, they constitute a pollution of the workenvironment.

Besides the infrared welding of plastic, such infrared radiators arealso used for preheating or pre-plasticizing of plastic components incombination with the vibration welding. The course of the procedure ofthe infrared welding is similar to the heated tool welding of plastics.In contrast to the heated tool welding, the welding zones of bothplastic joint partners are heated contactless by absorption of the heatradiation energy. In this way, a material residue emerging from theadhesion of the melting or molten material of the plastic components atthe heating element is avoided. As the joint areas of the plasticcomponents to be joined to each other are in most cases formed unevenlyand underlie further certain tolerances, the distance of specificsections of the plastic components to the heat radiator is irregular.This results in an inhomogeneous heating of the welding zone, i.e. ofthe portions of the plastic components to be heated.

After achieving a desired thickness of the melting layer on the plasticcomponent, the heating phase of the infrared radiator is replaced by thejoining phase. In doing so, the radiator element is moved away from thejoining plane or from the vicinity of the plastic components,respectively. The joining phase of the plastic components starts withthe mutual contact of the joining areas. While the joining areas arepressed against each other, a cooling takes place and thereby ahardening/curing and connecting of the plastic components. As soon asthis connection is produced, the infrared welding is completed.

At infrared welding, different radiator types are used depending on theapplication. These radiator types are for example short-wave radiatorshaving a wavelength of 1.6 μm as for example halogen radiators. Further,medium-wave radiators having a wavelength of between 1.6 μm and 3.5 μmare used, as for example metal foil radiators. Long-wave radiatorsprovide a further alternative, which cover a wavelength range of above3.5 μm, as for example quartz radiators. In this context it should bementioned that a thermal radiator does not emit the heat radiationexactly at one wavelength but instead in a wavelength range. Also, theabsorption characteristics of the plastics and thus the heating of thejoining zone may be very different. A main advantage of the infraredwelding is thus the missing contact between the heat source and theplastic, whereby a pollution of the heat source by means of plasticdeposits is avoided. A further advantage is the usage of the infraredradiator or in general the heat radiator as a preheating source in otherplastic-processing methods. At the vibration welding, for example, theplastic is preheated in the welding joint area by means of infraredradiation to increase the speed of the vibration welding in this way.For heating complex, i.e. three-dimensional and long, weld seamgeometries by means of an infrared radiator or for welding them,respectively, multiple radiators are often necessary. Further, it istechnically advantageous to limit the length of the radiators. Theshorter the heat radiators are the lower is the technical effort toreplace them in case of damage. In the first place, it is advantageousthat lots of small radiator elements facilitate a more homogeneousheating of the plastic components. Each of these radiator elements maybe adapted separately and independently from the remaining radiatorelements ideally to the respective portion of the plastic component tobe heated. At large plastic components, for example twenty or more heatradiator elements are required.

When using metal foil radiators it is a disadvantage that the metal foilof the metal foil radiator is freely accessible and thus subject tocertain safety requirements as voltage carrying element. To fulfilthese, sophisticated safety measures are necessary so that the workercannot touch the metal foil. Advantageously, metal foil radiators areadaptable to the surface contour of a plastic component with low effort.

It is thus an object of the present invention to provide a heatradiator, a device for infrared welding as well as a method for heatingor welding plastic components which are flexible and economicallyfeasible compared to known constructions and methods.

SUMMARY

The above-mentioned object is solved by a heat radiator according toindependent claim 1, a device for infrared welding of at least twoplastic components according to independent claim 2 as well as a methodfor heating or welding at least one plastic component according to theindependent patent claim 8. Advantageous embodiments and developments ofthe present invention result from the dependent claims as well as thedescription in combination with the respective drawings.

The heat radiator according to the invention, especially an infraredradiator, comprises the following features: at least one radiationsource by means of which electrical energy input is transformable intoheat radiation, and a control comprising at least one frequencyconverter having a first, a second and a third output so that betweenthe first and the third output a first alternating current and betweenthe second and the third output a second alternating current isprovidable, by means of which the at least one radiation source or aplurality of radiation sources is operable.

Heat radiators are used on the one hand for heating plastic componentsfor preparing for example the vibration welding. A further field ofapplication is the infrared welding of plastic components. Here, theheat radiators are used for a contactless heating of the plasticcomponents joined to each other subsequently.

Such heat radiators and according to a preferred embodiment, infraredradiators or metal foil radiators represent in the electric view ohmicloads. If such heat radiators are connected to an electric voltage, anelectric current flows through the heat radiator which is converted inthe heat radiator into heat radiation. Especially metal foil radiatorsare suitable for heating and welding plastic components as they can beadapted ideally to a component geometry alone or in combination withseveral metal foil radiators. However, as the current carrying metalfoil of the metal foil radiator is freely accessible, the electricvoltage on the metal foil represents a health risk for the worker incase of contact with the heat radiator.

For minimizing this risk, the heat radiator is driven according to theinvention by means of at least one frequency converter. Known frequencyconverters are used for driving rotary current motors, wherein thefrequency converter is connected to a three-phase network having athree-phase alternating voltage. To this end, voltage-lead frequencyconverters are used at most, which supply with their three outputs U, V,W the respective three inputs of a rotary current motor. In contrast tothis known frequency converters, the frequency converter used accordingto the invention supplies a first and a second alternating current usedfor operating and driving at least one or a plurality of heat radiators.The first alternating current is tappable or supplied between the firstand the third output of the frequency converter and the secondalternating current is tappable or supplied between the second and thethird output of the frequency converter. These different first andsecond alternating currents, which may also be equal with respect to theabsolute value, are usable for driving one or several heat radiators,especially metal foil radiators. The first and the second alternatingcurrents are provided by means of the frequency converter in combinationwith a respective first and second alternating voltage. For influencingthe operation of the metal foil radiator in a positive way, the firstand the third output of the frequency converter and/or the second andthe third output of the frequency converter are each connected to atransformer for transforming the electric alternating voltagerespectively provided by the frequency converter into a predefinedoperating range. This operating range is preferably above or below theelectric output voltage of the frequency converter. Preferably, at leastone of the transformers is used for transforming the electricalternating voltage of the frequency converter into a low voltage rangewhich is thought of being contact-proof. This means in particular thatfor example a worker may touch a metal foil radiator which is connectedto such a contact-proof electrical voltage. Because this contact-proofelectrical voltage, which is for example in a range below 40 V or below25 V, does not lead to health damages of the worker coming into contacttherewith. In this context it has to be emphasized that besides thefrequency converters operated with the three-phase alternating voltage,it is also preferred according to the invention to use a frequencyconverter operated with a one-phase alternating voltage. Duringoperation of the frequency converter operated with a one-phasealternating voltage, the respectively programmed control circuit of thefrequency converter (see below) ensures that two current outputs havingthe respective alternating voltages are provided at the output of thefrequency converter. From this it follows that the electrical supply ofthe frequency converter operated with one-phase alternating voltagecompared to the frequency converters operated with three-phasealternating voltage is different but at the output of the frequencyconverter operated with the one-phase alternating voltage the sametechnical features and requirements, respectively, like electricalalternating currents and electrical alternating voltages, are present asat the frequency converter operated with the three-phase alternatingvoltage.

Based on the above described driving of a heat radiator by means of afrequency converter especially adapted thereto, the present inventionalso comprises a device for infrared welding of at least two plasticcomponents. This device for infrared welding comprises the followingfeatures: at least one radiation source by means of which suppliedelectrical energy is convertible into heat radiation, especially a metalfoil radiator, and by means of which plastic components are heatable, acontrol comprising at least one frequency converter having a first, asecond and a third output so that between the first and the third outputa first alternating current and between the second and the third outputa second alternating current are producible for supplying the at leastone radiation source, and an assembly for holding and moving the plasticcomponents so that they are movable into abutment and weldable to eachother or they are movable to a further processing site after heating bymeans of the at least one radiation source.

The device for infrared welding of at least two plastic componentsaccording to the invention is based on the same components as the abovedescribed heat radiator. Therefore, the above technical characteristicsof the heat radiator and the frequency converter used in combinationtherewith apply in the same manner to the here mentioned device forinfrared welding.

As has been already discussed above, an ideal adaption of the radiatorgeometry to the component geometry is realizable with a plurality ofheat radiators or metal foil radiators. The usage of many small heatradiators has the further advantage that they may be operated with alower electrical voltage as for example elongated radiator segments.Thus, by means of the segmentation of the heat radiator or due to theusage of a plurality of small heat radiators, as for example metal foilradiators, the required electrical supply voltage is lowered topreferable 25 V alternating voltage or below. Thus, one is in the rangeof electrical low voltages so that machines and welding tools may berealized with lower safety requirements and thus easier. As anunintentional contact of an open metal foil radiator by the worker doesnot lead to an electrical surge dangerous to health.

For driving each heat radiator or each heat radiator segmentindependently, each segment has been driven with its own current andvoltage supply up to now. This results in a substantial effort due tothe high number of current power supplies. Further, each current powersupply requires its own control which results economically in hardlyacceptable costs. Therefore and according to the invention, it ispreferred that the first and/or the second transformer comprises aprimary winding and one or a plurality of secondary windings in order tobe able to electrically supply one or a plurality of radiation sources.To this end, the secondary windings are adapted in their number to thenumber of the heat radiators to be supplied electrically. Further, thetransformation ratio of primary windings to secondary windings isdimensioned so that the ideal electrical operating range for the heatradiator to be driven, for example the metal foil radiator, isachievable. Thus, an electrical extra-low voltage is producible,preferably by means of a suitable dimension of the secondary winding, bymeans of which a metal foil radiator may be operated contact-proof. Inthe same way it is preferred to adapt the secondary winding or thesecondary windings to an electrical supply of a plurality of metal foilradiators. Because depending on the electric interconnection of severalmetal foil radiators, which act as ohmic load in an electrical currentcircuit, known calculation instructions are applicable which guarantee adesired electrical operation range or supply range of each metal foilradiator.

Corresponding to this general summary of the present invention, thefrequency converter acts as current power supply which is able to supplytwo current strengths which are independent from each other and may bedifferent or equal in value. In combination with the above-mentionedtransformers, contact-proof electrical operating voltages are alsoproducible for the at least one radiation source.

According to a preferred embodiment of the present invention, any typeof a heat radiator is usable in combination with the above describedcircuit. Preferably, a metal foil radiator or a plurality of metal foilradiators is used as heat radiator according to the invention.

According to a further preferred embodiment of the present invention, aplurality of frequency converters is used for electrically supplying theheat radiators. This plurality of frequency converters is connected witheach other and drivable via a BUS-system (Binary Unit System). Such aBUS-system ensures that each frequency converter is drivable in aneffective manner individually. Further, the circuit effort for realisingsuch an individual driving of the frequency converters is limited due tothis BUS-system. Further and due to the individual driving of each metalfoil radiator via the BUS-system, different distances between theplastic component and the heat radiator are compensable not only by anincreased number of heat radiators but also by means of individualdifferent driving of each heat radiator in different component segments.

The present invention discloses also a method for heating or welding atleast one plastic component. This method comprises the following steps:providing (S1) at least one radiation source, preferably at least oneinfrared heat radiator or a metal foil radiator, electrically supplying(S2) the at least one radiation source by means of at least onefrequency converter producing a first and a second alternating current,and heating (S4) the at least one plastic component by means of adefined alternating current in the at least one radiation source.

According to the above description, the metal foil radiators aresupplied with an individual adaptable electrical voltage and acorresponding alternating current. These electrical alternating currentsare provided by at least one frequency converter working as anelectrical power supply with two different or equal providable currents.By means of transformers (S3), preferably downstream of the frequencyconverter, a contact-proof alternating voltage is produced for theelectrical supply of the at least one radiation source.

For specifically heating two plastic components and welding them to eachother subsequently, preferably the heat radiators are driven (S5) via aBUS system. After sufficient plasticising of the plastic components inthe welding zone, the at least two heated plastic components are movedinto abutment with each other so that the plastic components are beingwelded (S6) to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of preferred embodiments and bestmode will be set forth with reference to the accompanying drawings, inwhich:

FIG. 1 shows a first preferred embodiment of the present invention bymeans of which four heat radiators are driven,

FIG. 2 shows a further preferred embodiment of the present invention bymeans of which two heat radiators are driven,

FIG. 3 shows a further preferred embodiment of the present invention bymeans of which a plurality of heat radiators is driven and

FIG. 4 shows a flowchart of a preferred embodiment of the method forheating or welding at least one plastic component according to theinvention.

DETAILED DESCRIPTION

The present disclosure is related to at least one heat radiatorelectrically operated by means of a frequency converter. As has beenexplained above already, different constructions of heat radiators areknown converting the supplied electrical energy into a heat radiation.By means of this heat radiation, plastics and other materials are heatedor preheated and thus prepared for the further processing. Also,plastics are welded to each other by means of such heat radiators,especially infrared heat radiators. Such methods are known as infraredwelding of plastics. In the following, the usage, the driving, theoperation of heat radiators is explained by means of metal foilradiators. Therefore, all explanations apply also to other heatradiators.

The preferred metal foil radiator is known from the prior art. Arespective construction is described in DE 42 42 812 A1 to which it isreferred to with respect to the structure and functional principle ofthe infrared radiator. It consists of a metal foil to which anelectrical voltage is supplied, preferably an electrical alternatingvoltage. The thus resulting current flow in the metal foil, which actsas ohmic resistance in the current circuit, is converted into heatradiated by the metal foil. The metal foil radiators are producible innearly any random size and shape, whereby nearly any arbitrary surfacecontour is radiatable with heat, preferably evenly, by means of aplurality of metal foil radiators. Based on this heat supply, plasticsare preheatable or infrared weldable. The preheating by means of aninfrared radiator in connection with the plastic welding is explained inDE 197 52 648 C2. DE 101 22 802 A1 describes a radiator construction anda method for preheating plastic components in combination with the knownvibration welding or friction welding. The description of an infraredradiator as well as its usage in infrared welding or plastic welding isalso extractable from DE 601 10 536 T2. It is referred to theabove-mentioned documents concerning the construction of infraredradiators as well as the design, the course of preheating methods andplastic welding methods and their combination.

For driving the plurality of the metal foil radiators required forheating or infrared welding, according to the invention at least onefrequency converter is used in combination with a transformer ordirectly without interconnected transformer. Depending on the number ofmetal foil radiators to be driven, several frequency converters are usedwhich are each supplied with a known three-phase alternating voltage orwith a one phase alternating voltage.

Known frequency converters are generally used for controlling threephase induction motors. In doing so, the frequency of the alternatingvoltage supplied to the three phase induction motor is varied forchanging the number of revolutions of the three-phase motor. Thisprinciple is also called voltage led frequency converter, which hasgained acceptance in broad application since the 1990s.

Such frequency converters and also frequency converters operated withone phase comprise a rectifier which produces a direct voltage from analternating voltage, for example the supplying three-phase alternatingvoltage. This direct voltage is stabilized and smoothed in a downstreamintermediate circuit. Then, and depending on the requested number ofrevolutions of the motor, the required voltage-frequency-ratio in theform of an alternating voltage is produced in an inverter. The threecomponents rectifier, intermediate circuit and inverter are drivenindividually and/or commonly via a superior control circuit. In knownfrequency converters, the control circuit specifies the necessaryinformation for producing the number of revolutions in the motor andthus for producing the respective voltage-frequency-ratio in thefrequency converter.

For driving the preferred plurality of metal foil radiators, a frequencyconverter is used with modified functionality compared to the knownthree-phase and one-phase frequency converters (see above). Because ametal foil radiator represents an ohmic load in a current circuit, whichhas not to be driven with an individually adaptedfrequency-voltage-ratio. The frequency converter has thus not the objectto vary a frequency or to provide a variable frequency. Instead, thefrequency converter operates as a dual current source or currentcontrol, at the output of which two individually controlled currents areprovided. In doing so, it is especially advantageous that the frequencyat the output of the frequency converter is adjustable. In this way, anoptimal syntonization or tuning to the transformers connected downstreamis achieved. As the frequency converter has the three outputs U, V, W, afirst current is provided between the outputs U and V and a secondcurrent is provided between the outputs W and V. In this circuit, atotal or summation current flows off preferably via V.

Requirement for the usage of frequency converters for the current supplyto metal foil radiators is the development of respective software whichis used in the control circuit of the frequency converter. This softwareensures that one of the three outputs of the frequency converter can beused for the flow off of the total current of the other two outputs.Further, this software ensures an appropriate current control in thefrequency converter as the metal foil radiators working as ohmic loadshave to be controlled via the current. It is preferred to realize thecurrent control by means of a PI-controller. Certainly, also othercontrollers as for example a PID-controller are usable. Furthermore,this software contains several monitoring functions. In this context, itis for example preferred to monitor the electric output voltages at thefrequency converter. In this way, it can be ensured that the electricalvoltage supplied to the metal foil radiator, preferably a contact-prooflow voltage of 25 V, is not exceeded even in case of failure. In thisway, a risk for the health of a worker by means of electricalovervoltages is avoided.

The electrical output voltage of the frequency converter is preferablyin the range of the input voltage, for example at 400 V in Germany.Three-phase networks in other countries supply other input voltages sothat here also other output voltages are preferred, respectively. Inmost countries in Europe, the three-phase network supplies 400 V like inGermany. While in Mexico and Brazil the input voltage is also 400 V, theinput voltage in India is 440 V and in the USA 480 V. In Japan, theinput voltage of the three-phase network is 200 V.

In contrast thereto, the output current of the frequency converter isdefined by the power of the frequency converter. Here, the advantage ofusing a transformer at the output of the frequency converter can beseen. In the same extent as the electrical voltage of typically 400 V istransformed to lower electrical voltages, the available electricalcurrent increases. This electrical current strength is, however, at thepreferred contact-proof low voltages of for example 25 V not dangerousto the health of a person touching the metal foil of the metal foilradiator.

Basically, a voltage control instead of the above-mentioned currentcontrol in the frequency converter is possible. Therefore, the differentelectrical resistances in the operating current circuit of the metalfoil radiator have to be known or to be determined first, as for exampletransition resistance, line resistance, temperature dependingresistances of the radiator. Without these values, which can only bedetermined with great effort, a precise voltage control cannot beensured. Such an effort is omitted at the preferred and above describedcurrent control by means of the frequency converter.

FIGS. 1-2 show different exemplary preferred embodiments of theinvention in which metal foil radiators 40; 42; 44; 46; 48; 50 ofdifferent size and/or type are driven. These metal foil radiators 40;42; 44; 46; 48; 50 are supplied electrically via the frequency converter10 in combination with a transformer 30; 32; 34 of differentconfiguration or directly without transformer. The frequency converter10 in turn is supplied by a connected preferred three-phase network,especially a three-phase power connection, designated with the referencesign 70. In the same way, the three-phase power connection 70 could alsobe a one-phase power connection (not shown), which is also preferredaccording to the invention. While here the frequency converter 10 can bedriven individually, for example via a separate control line or controlcircuit, it is also preferred to supply the frequency converter withcontrol information and operation information via a BUS-system 60, forexample a CAN-Bus or a PROFI-Bus. Additionally to the BUS-system 60 orin combination with the BUS-system 60, individual frequency converters10 communicate directly with each other. In this context it is preferredto operate one frequency converter 10 as master and the frequencyconverters 10 connected thereto as slave (see FIG. 3). In this case, thefrequency converters 12 defined as slave follow the control commandswhich have been received by the master frequency converter 10 via theBUS-system 60 or any other connection.

In FIG. 1, four metal foil radiators 40 a, 40 b, 40 c, 40 d are operatedvia the frequency converter 10 and the two transformers 30 a, 30 b. Asdual current source, the frequency converter 10 provides two individualcurrent strengths between the outputs U and V as well as W and V. It isalso preferred to tap the currents between the outputs U and W as wellas V and W. The alternating voltages of preferably around 400 V providedat the outputs U and V as well as W and V are transformed into a desiredelectrical voltage-operating range of the connected metal foil radiators40 a-d by two identical transformers 30 a, 30 b. The general object ofthe transformers 30 is thus the stepping down of the output voltage ofthe frequency converter 10 to lower electrical voltages whilesimultaneously increasing the possible output currents. Because due tothe usage of lower electrical voltages, the safety instructions aresatisfied automatically. At the same time, higher electrical currentsare available for which otherwise a more powerful frequency converter 10has to be used. In case the official threshold value for contact-proofelectrical low voltages should change, preferably the transformer 30 mayalways be adapted correspondingly in combination with the connectedmetal foil radiator or radiators.

It has been seen in the practical application that the usage oftransformers 30 with at least two equal secondary windings, and thus foreach metal foil radiator 40 one secondary winding, is advantageous.Thus, the transformers 30 can be adapted variably to the metal foilradiators 40; 42; 44; 46; 48; 50 to be supplied via the secondarywindings. Thus, the usage of normalized components as for example thefrequency converter 10 is also possible. Generally, the transformers areindicated with the reference signs 30, 30 a, 30 b, 30 c and 32. At theinput of a transformer, the frequency converter 10; 12 supplies theprimary winding (not shown) of the transformer 30, 30 a, 30 b, 30 c and32. The size of the secondary winding as well as the number of thesecondary windings is given symbolically by means of the shown voltagevalue “25 V” at the output of the transformer.

FIG. 1 shows the usage of the transformers 30 a, 30 b with two identicalsecondary windings. Thus, four metal foil radiators 40 are drivable intotal. For simplifying the electrical supply and interconnection of themetal foil radiators 40 a-d, it is preferred that the two metal foilradiators 40 a, 40 b, 40 c, 40 d supplied by the same transformer 30 a,30 b have the same current consumption and voltage consumption. In thiscontext, the electrical resistance of the metal foil radiator 40 a; 40b; 40 c; 40 d is the defining factor. This electrical resistance of thetwo infrared radiators 40 a; 40 b and 40 c, 40 d should be almostidentical. This is given in general if both metal foil radiators 40 a,40 b, 40 c, 40 d are configured identical, for example having the samewidth and length.

It is also preferred that the metal foil radiators 40 c, 40 d are largeror smaller, thus longer or shorter or narrower or wider than the metalfoil radiators 40 a, 40 b of the first transformer 30 a. As for examplein case of larger metal foil radiators 40 c, 40 d, the ohmic resistancethereof is also higher as at the metal foil radiators 40 a, 40 b, sothat the current provided by the second transformer 30 b must also belarger. These different current strengths are supplied to the twotransformers 30 a, 30 b by the frequency converter 10 according to theconnected metal foil radiators 40 a, 40 b and 40 c, 40 d. In this way,each metal foil radiator 40 a, 40 b, 40 c, 40 d may be supplied with theappropriate electrical power despite a preferred contact-proof lowvoltage of 25 V. Because the electrical power is calculated by theproduct of the electrical voltage present at the metal foil radiator andthe flowing electrical current. Thus, and at constant low voltage, theelectric current would be increased by the frequency converter 10 tosupply a metal foil radiator with higher power or performance.

It is certainly also preferred to supply the metal foil radiator 40 a to40 d with a higher electrical voltage than the contact-proof voltage.

With respect to FIG. 2, an also preferably used driving of metal foilradiators 42 is shown. The frequency converter 10 drives only twoindependently operated metal foil radiators 42 via the two transformers30. The transformers 30 comprise one primary winding in combination withtwo secondary windings, respectively, for producing low voltages, justlike the transformers 30 a and 30 b from FIG. 1. As can be seen based onthe connection between the transformer 30 and the metal foil radiator42, the outputs of the two secondary windings of the transformers 30 areconnected in series to provide a higher electrical voltage to theconnected metal foil radiator 42. Such an electric circuit is preferablyused at longer metal foil radiators 42. These longer metal foilradiators 42 require a higher supply voltage compared to shorter metalfoil radiators.

Certainly, this electric circuit is also realisable by means of atransformer (not shown) having only one secondary winding. This only onesecondary winding would then be adapted in its number of windings to therequired higher electrical supply voltage for the connected metal foilradiator 42. It is also preferred to supply a metal foil radiator 46 bymeans of the transformers 30 from FIG. 2 which has a higher electricalpower and thus a higher electrical current consumption. To ensure thishigher power of the metal foil radiator 46 (see FIG. 3) via thetransformer 30 in accordance with the contact-proof electrical lowvoltage of for example 25 V, the metal foil radiator 46 has to besupplied with a higher electrical current compared to the metal foilradiator 42 from FIG. 2. To this end, both secondary windings of thetransformer 30 c being identical to the secondary windings of thetransformer 30 from FIG. 2 are connected parallel to each other. Thisconnection of the outputs of the secondary windings of the transformer30 c leads to an addition of the current strength provided at theoutputs of the secondary windings of the transformer 30 c. At the sametime, however, the electrical voltage remains constant. It followstherefrom that by means of the connection between the transformer 30 cand the metal foil radiator 46 according to FIG. 3, a more powerfulmetal foil radiator 46 can be supplied while simultaneously maintainingthe contact-proof electrical low voltage.

FIG. 3 shows a further preferred embodiment of the driving of severalmetal foil radiators. In this assembly, different driving concepts arecombined with each other. Further, it is exemplarily shown thatdifferent frequency converters 10, 12 may be combined with each othervia the above mentioned BUS-system 60. According to an alternative, eachfrequency converter 10, 12 is connected to the BUS-system 60 andreceives therefrom its individual control information and controlcommands.

According to a further alternative, one frequency converter acts asmaster frequency converter. This master frequency converter 10 isconnected to the BUS-system 60. The further frequency converters 12 inFIG. 3 are configured as slave frequency converters. These slavefrequency converters 12 follow the control information to the masterfrequency converter 10. In this case, the slave frequency converters 12are not connected to the BUS-system 60. Instead, they receive theircontrol information directly from the master frequency converter 10 asindicated by the connection lines 65.

In the assembly of FIG. 3, different control concepts for differentmetal foil radiators 40, 42, 44, 46, 48, 50 are combined with eachother. It is thus stressed that any component configuration or componentsurface of plastic components are radiatable with heat by combiningdifferent types of metal foil radiators 40, 42, 44, 46, 48, 50 with eachother so that the component surface of the plastic components is coveredideally by the metal foil radiator. Thus, and for example, the frequencyconverter 10 from FIG. 3 is connected to two transformers 30, the supplyof which to metal foil radiators 40, 42 was already explained incombination with FIGS. 1 and 2. Thus, the first transformer 30 operatespreferably two electrically equal metal foil radiators 40 while thesecond transformer 30 operates only one metal foil radiator 42. Thismetal foil radiator 42 is, however, supplied with the double electricalvoltage by connecting both outputs of the secondary windings of thesecond transformer 30 in series.

The frequency converter 12 arranged in the centre of FIG. 3 is connectedto a transformer 32 supplying preferably the electrically equallyconfigured metal foil radiator 44. To this end, the transformer 32compromises one secondary winding for each connected metal foil radiator44, respectively. Thus, it is also preferred to combine in principle anynumber (N) of secondary windings in the transformer 32 with the primarywinding. However, it should be considered that the current provided atthe transformer 32 by the frequency converter is distributed to theindividual secondary windings for the supply of the metal foil radiator42. This results in that the power provided by the frequency converter12 at the output U-V is splitted among the N secondary windings. Thissplitted electrical power has to be sufficient large to operate theconnected metal foil radiator 44 adequately.

At the transformer 30 c, both present secondary windings are connectedin parallel. In this way, the electrical current strengths provided bythe secondary windings are added so that the connected metal foilradiator 46 can be supplied, indeed, with the preferred low voltage butsimultaneously with an increased electrical current strength.

The further preferred driving possibility of metal foil radiators 48, 50is shown by the frequency converter 12 at the right picture margarine ofFIG. 3. The here depicted transformer 34 comprises only one secondarywinding compared to the remaining transformers 30 a, 30 b, 30, 32, 30 cwhich is adapted to the connected metal foil radiator 48. By using onlyone secondary winding, the connection facility for several metal foilradiators at the transformer 34 is lost but the electrical supply of themetal foil radiator 48 can be realised ideally. Because the electricalcurrent provided by the frequency converter 12 as well as the electricalvoltage realised by the transformer 34 correspond exactly to theconnected metal foil radiator 48 for realising its ideal electricalpower.

A metal foil radiator 50 is connected directly to the second currentoutput between the outputs W and V of the frequency converter 12 withoutinterconnection of a transformer. By means of this electrical circuit,the full output voltage supplied by the frequency converter can be usedby the metal foil radiator 50. At the same time, the electrical currentsupplied by the frequency converter is lower as compared to atransformer interconnected between the frequency converter 12 and themetal foil radiator 50. Especially, at long metal foil radiators, thusmetal foil radiators having a high ohmic resistance, such a driving asused at the metal foil radiator 50 is useful. Further, it is preferredto use such a driving in case these metal foil radiators are notaccessible by a worker. In this case, it is not required that the metalfoil radiator 50 is operated with a contact-proof electrical lowvoltage.

Each of the here shown or suggested driving concepts for metal foilradiators in combination with a frequency converter and a transformer orwithout transformer are randomly combinable with any other drivingconcept. Thus, and for example, a not shown driving concept consists inthe use of a transformer having five secondary windings for operatingfive electrically equal metal foil radiators. In parallel thereto, ametal foil radiator may be connected directly to the frequency converterwithout an interconnected transformer. It is also preferred to transformthe electrical operating voltage upwards by means of the interconnectedtransformers. This would then require respective heat radiators whichcan be operated with non-contact-proof low voltages.

Solely with the standard configurations of a frequency converter 10having two transformers 30 with two secondary windings, respectively,six different preferred circuitry and connection alternatives of heatradiators or metal foil radiators result.

-   -   four metal foil radiators, two of which having the same supply        current and the same supply voltage,    -   three metal foil radiators, two of which having the same supply        current and the same supply voltage and one metal foil radiator        having maximally the double supply voltage,    -   three metal foil radiators, two of which having the same supply        current and the same supply voltage and one metal foil radiator        having maximally the double supply current,    -   two metal foil radiators, one metal foil radiator thereof having        the double electrical supply voltage and one metal foil radiator        having the double electrical supply current,    -   two metal foil radiators having the double electrical supply        current and    -   two metal foil radiators having the double electrical supply        voltage.

At a transformer having N secondary windings (for example thetransformer 32 in FIG. 3), up to N metal foil radiators may be connectedthereto. These N metal foil radiators are operated with the samecurrent. In the easiest case with N=1, only one metal foil radiator isarranged in the secondary circuit of the transformer 30. In principle,the number of the metal foil radiators N may be increased arbitrarily sothat then three, four or more metal foil radiators may be supplied viathe frequency converter in combination with the transformer.

Disadvantageous in using transformers are their magnetisation losses. Byproviding the electrical voltage at the input of the transformer assinus signal with high-frequency, this problem is minimised. Becausewith increasing frequency of this sinus signal of the electrical inputvoltage, the magnetisation loss decreases. In this manner, a smallertype of transformer may be used. In this context it is preferredaccording to the invention to use the frequency of 300 Hz, wherein thiscomprises a compromise between control speed of the frequency converterand a frequency as high as possible for reducing the magnetisationlosses. In this context it is, however, also preferred to use otherfrequencies.

When using high electrical currents and low electrical voltages at themetal foil radiator, the usage of low voltage transformers isadvantageous. Preferably, the low voltage transformers transform theoutput voltage of the frequency converter 10 into an alternating voltagerange of 0 V to 50 V and according to a further preferred embodimentinto a range of 0 V to 25 V. Indeed, the transformers are additionallyrequired but due to their usage a significantly smaller and cheaperfrequency converter may be chosen for the current supply.

The above described circuit concepts are used for heating and/orinfrared welding of plastic components. To this end, the plurality ofthe metal foil radiators is driven according to the above concepts sothat they emit their heat radiation to the adjacently arranged plasticcomponents. For radiating the plastic components ideally with heat, itis preferred to hold these plastic components in an appropriate assemblyand/or moving them with this assembly towards the heat radiators or awaytherefrom. Such an assembly thus brings the plastic component inimmediate proximity to the metal foil radiators so that heat impinges inthe surface area of the plastic component. After the plastic componenthas been heated sufficiently, the assembly moves the plastic componentfor further processing to a second plastic component, for example, toweld it thereto. For this purpose, both plastic components are pressedagainst each other in their heated joint zones so that after cooling ofthe joint zones a connection between these two plastic components ispresent. This proceeding is generally known as infrared welding.

1. A heat radiator, especially an infrared radiator, comprising: a. atleast one radiation source by means of which supplied electrical energyis convertible into heat radiation, and b. a control comprising at leastone frequency converter having a first, a second and a third output sothat between the first and the third output a first alternating currentis providable as well as between the second and the third output asecond alternating current is providable by means of which the at leastone radiation source is operable.
 2. The device according to claim 1,wherein between the first and the third output of the frequencyconverter a first transformer and/or between the second and the thirdoutput of the frequency converter a second transformer is connected bymeans of which an alternating voltage provided by the frequencyconverter is transformable into an electrical operating range of the atleast one radiation source.
 3. The device according to claim 2, theradiation source of which is a metal foil radiator or a plurality ofmetal foil radiators.
 4. The device according to claim 2, wherein thefirst and/or the second transformer comprises one primary winding andone or a plurality of secondary windings for supplying one or aplurality of radiation sources.
 5. The device according to claim 4, theradiation source of which is a metal foil radiator or a plurality ofmetal foil radiators.
 6. The device according to claim 4, wherein atleast one of the secondary windings is configured in view of the primarywinding so that a contact-proof electrical operating voltage for the atleast one radiation source is producible.
 7. The device according toclaim 6, wherein the radiation source of which is a metal foil radiatoror a plurality of metal foil radiators.
 8. The device according to claim1, comprising a plurality of frequency converters which are connected toeach other and drivable via a BUS-system.
 9. The device according toclaim 7, comprising a plurality of frequency converters which areconnected to each other and drivable via a BUS-system.
 10. A device forinfrared welding of at least two plastic components, comprising: atleast one radiation source by means of which supplied electrical energyis convertible into heat radiation and by means of which plasticcomponents are heatable, a control comprising at least one frequencyconverter having a first, a second and a third output so that betweenthe first and the third output a first alternating current is producibleas well as between the second and the third output a second alternatingcurrent is providable for supplying the at least one radiation source,and an assembly for holding and moving the plastic components so thatthey are movable into abutment and weldable to each other or movable toa further processing site after the heating by means of the at least oneradiation source.
 11. The device according to claim 10, wherein betweenthe first and the third output of the frequency converter a firsttransformer and/or between the second and the third output of thefrequency converter a second transformer is connected by means of whichan alternating voltage provided by the frequency converter istransformable into an electrical operating range of the at least oneradiation source.
 12. The device according to claim 11, wherein thefirst and/or the second transformer comprises one primary winding andone or a plurality of secondary windings for supplying one or aplurality of radiation sources.
 13. The device according to claim 12,wherein at least one of the secondary windings is configured in view ofthe primary winding so that a contact-proof electrical operating voltagefor the at least one radiation source is producible.
 14. The deviceaccording to claim 13, comprising a plurality of frequency converterswhich are connected to each other and drivable via a BUS-system.
 15. Amethod for heating or welding at least one plastic component, the methodcomprising the following steps: a. providing at least one radiationsource, preferably at least one infrared radiator or metal foilradiator, b. electrically supplying the at least one radiation source bymeans of at least one frequency converter producing a first and a secondalternating current, and c. heating the at least one plastic componentby means of a defined alternating current in the at least one radiationsource.
 16. The method according to claim 15, comprising the furtherstep: interconnecting a transformer between the frequency converter andthe at least one radiation source and producing a contact-proofalternating voltage for the electrical supply of the at least oneradiation source.
 17. The method according to claim 15, comprising thefurther step: driving a plurality of radiation sources via a pluralityof frequency converters which are connected to each other via aBUS-system.
 18. The method according to claim 16, comprising the furtherstep: driving a plurality of radiation sources via a plurality offrequency converters which are connected to each other via a BUS-system.19. The method according to claim 15, comprising the further step:moving at least two heated plastic components into abutment with eachother so that the plastic components will be welded to each other. 20.The method according to claim 18, comprising the further step: moving atleast two heated plastic components into abutment with each other sothat the plastic components will be welded to each other.